Fracture Behavior on SCC of API X52 Pipeline Steel Under Cathodic Protection

Abstract

This paper analyzes the fracture behavior and mechanisms of stress corrosion cracking (SCC) of API X52 pipeline steel. Susceptibility and mechanism of SCC was investigated using slow strain rate tests (SSRT) performed at strain rate of 1 × 10−6 in/sec in a glass autoclave containing a soil solution with pH of 8.5 at room temperature. Cathodic polarization potentials of −100, −200 and −400 mV referred to Ecorr was applied in order to establish the effectiveness of cathodic protection in mitigating SCC of X52 pipeline steel. To study the effects of several over potential in SSRT were performed at different cathodic potentials. The results of reduction area ratio (RAR), time to failure ratio (TFR) and plastic elongation ratio (PER) indicate that X52 pipeline steel was susceptible to SCC. Scanning electron microscopy (SEM) observations of these specimens showed a brittle type of fracture with transgranular appearance. The failure and SCC mechanism of X52 steel in the soil solution was hydrogen based mechanism. This mechanism was confirmed through the internal cracks observed in these specimens. All cracking tests indicated that the SCC rate was enhanced by plastic deformation.